This invention relates to a pressure relief valve and more particularly relates to a pressure relief valve particularly useful for venting a container for containing fluid which expands and becomes increasingly pressurized upon external heat being applied to the container.
Such pressure relief valves are particularly useful in venting over-the-road tankers in accordance with ICC regulations.
Numerous of such pressure relief valves are known to the art. For example, a pressure relief valve entitled SAFETY RELEASE PIPE CAP is disclosed in U.S. Pat. No. 4,139,005, patented Feb. 13, 1979, Gilbert C. Dickey, Inventor. One embodiment of the pressure relief valve disclosed in this patent includes a polypropylene ferrule of relatively low thermal conductivity and a fusible disc of mixed polymeric material typically consisting of an 80–20% by weight mixture of low density polyethylene and ethylvinylacetate. Such fusible disc is taught as melting at a predetermined temperature, 220° F.–250° F., to vent a container containing fluid expanding due to external heat being applied to the container. The heat from the container is conveyed to the fusible disc by direct engagement between the fusible disc and a vent pipe connected to the container. Since the ferrule is of a relatively low thermal conductivity material, the ferrule does not transfer, or at least does not substantially assist in transferring, heat from the container to the fusible disc.
Some pressure relief valves known to the art have a depressed or inwardly extending top which can form a cavity which tends to accumulate foreign matter such as dirt and other debris and, in winter, ice and snow. Such foreign matter can obscure the top of the pressure relief valve and if sufficiently severe can potentially, at least, inhibit the pressure relief function of the pressure relief valve.
It is believed there is need in the art for a new and improved pressure relief valve including an element of relatively high thermal conductivity in which a fusible member is mounted and which element of relatively high thermal conductivity enhances the conduction of heat to the fusible member. It is believed there is a further need in the art for a new and improved pressure relief valve having a smooth, or at least substantially smooth, top which inhibits the accumulation of foreign matter thereon such as the afore-noted dirt and other debris, and ice and snow occurring in winter.